1966 20 hp Johnson bogs down

[Jeaux]

Electric start. Motor starts easily, idles well. When throttle is opened wide, motor runs for 10-15 seconds, then bogs down (but does not die). If I back off throttle for a few seconds, then throttle up, I get full power for 5-10 seconds. Pattern repeats. Any suggestions?

 

[Chinewalker]

Re: 1966 20 hp Johnson bogs down

Hi Jeaux,<br /> Is it a sudden cut-off drop in power, or a gradual drop off? If it's a sudden drop off, my bet is ignition related (condenser? Points? Coil?, plug wires?). If it's gradual, look into the fuel system. (fuel pump keeping up flow at high speed? Partial blockage somewhere?)<br /> Localize the problem - find out what it isn't and go from there...<br />- Scott

 

[Jeaux]

Re: 1966 20 hp Johnson bogs down

I already replaced points-condensors-coils. Didn't fix the problem. A well-paid Mechanic did some work and said everything was working. I took it to the water and it ran for maybe 5 minutes before this "bog-down" pattern started. Before I pay the man again, I was hoping for some input.<br />You asked about how quickly it bogs down. The cut-out in power is not instantaneous, but is quick. I don't know if that helps or not.

 

[ehenry]

Re: 1966 20 hp Johnson bogs down

next time it does it reach back and pum on the primer bulb and see if that helps.

 

[Tracy Coleman]

Re: 1966 20 hp Johnson bogs down

Jeaux<br />On another tack, how is the cooling?, changed water pump impeller? Sometimes a leaking gasket can pressurize the water jacket where the engine will overheat at high speed but at slow speed the water pump pressure will overcome the exhaust leak pressure and run somewhat normal. Head gasket is suspect. Check for exhaust in the water passage by opening the thermostat (top of the cylinder head) and running the engine- look for bubbles and or blue smoke in the gushing water.<br />Backfire

 

[Jeaux]

Re: 1966 20 hp Johnson bogs down

Thanks all for the input. Is the impeller hard to get to on this model? I have replaced an impeller on an Evinrude Fleetwin (not too bad), but was unable to help a friend get into the impeller housing of his Gamefisher's. I guess I need to invest in a manual...Any recommendations on manuals? Chilton, Seloc, or ...?

 

[Tracy Coleman]

Re: 1966 20 hp Johnson bogs down

Jeaux<br />Very easy to do an impeller change. Get a manual, either one will do fine. Follow directions.<br />Backfire

 

[loganmallory]

Re: 1966 20 hp Johnson bogs down

is your fuel tank properly vented? make sure the vent isnt clogged.

 

[Jeaux]

Re: 1966 20 hp Johnson bogs down

I just pulled off the prop and put the motor in a tank. Started right up. In gear, went full throttle and stayed there without bogging down (The shop mechanic tests motors that way). The "bogging" problem apparently occurs only when under load. Does this narrow the list of possible causes any?

 

[Jeaux]

Re: 1966 20 hp Johnson bogs down

(and the fuel bulb stays hard while running)

 

[dgrimme]

Re: 1966 20 hp Johnson bogs down

Had the exact same problem with my 1999 25HP Merc. I added 1/2 bottle of Sta-bil to the 12-13 gallons of gas in the tank. Let it sit for a day so Sta-bil could go to work. Next day, hooked up the hose and muffs, and it ran like the day I bought it! By the way, my motor had previously not been run in a few months, so I think I was starting to experience gas problems. Don't know if your problem is the same, but Sta-bil will not hurt the gas and is a cheap remedy, just the same.

 

[Jeaux]

Re: 1966 20 hp Johnson bogs down

Thanks, Coleman. Will give i a try. Also, motor does run better if I remove shroud.

 

[Meaux]

Re: 1966 20 hp Johnson bogs down

Hey Jeaux<br /><br /> When removing the shroud, does the motor reach and maintain full power----or just slightly improve the running?? Is there an air filter on the air intake to the motor?? Is it clean??<br /><br />Meaux

 

[Jeaux]

Re: 1966 20 hp Johnson bogs down

It seems to maintain full power. Where would I look for an air filter? The motor seems only to have 8-10 tiny holes drilled in the plate that the power head sits on, to allow air inside the shroud.

 

[wilde1j]

Re: 1966 20 hp Johnson bogs down

There is no air filter on OB's, but when you say motor maintains WOT with the cover off, it strongly suggests an exhast leak. Check the exhaust cover first and look for any signs of exhaust leakage (gaskets, missing fasteners, etc.)<br />Jim

 

[Jeaux]

Re: 1966 20 hp Johnson bogs down

Thanks, WildeOne. I will check that out. I sure am learning more than I wish I needed to know about outboards!